Radiation image acquisition system

ABSTRACT

A radiation image acquisition system of an aspect of the present invention includes a radiation source emitting radiation toward an object, a holding unit holding the object, a wavelength conversion member generating scintillation light in response to incidence of the radiation emitted from the radiation source and transmitted through the object, a first imaging means condensing and imaging scintillation light emitted from an incidence surface of the radiation of the wavelength conversion member, a second imaging means condensing and imaging scintillation light emitted from a surface opposite to the incidence surface of the wavelength conversion member, a holding unit position adjusting means adjusting the position of the holding unit between the radiation source and the wavelength conversion member, and an imaging position adjusting means adjusting the position of the first imaging means.

TECHNICAL FIELD

The present invention relates to a radiation image acquisition system.

BACKGROUND ART

Conventionally, as described in the following Patent Document 1, thereis known a device which irradiates a tabular scintillator with X-raysemitted from an X-ray source and transmitted through an imaging object,detects visible light (scintillation light) generated in thescintillator by solid-state photodetectors laminated on both surfaces ofthe scintillator, and superimposes image signals output from therespective solid-state photodetectors on each other to acquire aradiation image. In this device, photodetecting elements are coupled toan X-ray incidence surface of the scintillator and its back surface, andthe detection efficiency for visible light is enhanced by detectingvisible light in each of the photodetecting element on the incidencesurface side and the photodetecting element on the back surface side.

Also, as described in the following Patent Document 2, there is known adevice which, by use of two scintillators overlaid with each other andone detector, detects scintillation light emitted from the scintillatoron an incidence surface side by one surface of the detector, and detectsscintillation light emitted from the scintillator on the opposite sideby the other surface of the detector. In this device, images are formedwith two types of different wavelengths on the respective surfaces ofthe detector.

CITATION LIST Patent Literature

Patent Document 1: Japanese Patent Application Laid-Open No. H07-27866

Patent Document 2: Japanese Translation of International Application No.2000-510729

SUMMARY OF INVENTION Technical Problem

Meanwhile, because the X-ray source is a spot light source, it isnecessary for the object to be disposed in at least a region that isirradiated with X-rays. For example, when the object to be imaged islarge, and a full picture of the object is desired to be captured, it isnecessary to dispose the object at a position closer to thescintillator. By bringing the object close to the scintillator, theprojection magnification ratio with respect to the scintillator can belowered, which allows having a full picture of the object within therange of the scintillator.

The present inventors have diligently studied a radiation imageacquisition system including a first imaging means that condenses andimages scintillation light emitted from an X-ray incidence surface of ascintillator and a second imaging means that condenses and imagesscintillation light emitted from a surface opposite to the incidencesurface. In such a radiation image acquisition system, the first imagingmeans, i.e., the imaging means on the incidence surface side is locatedon the same side as that of the object with reference to thescintillator.

When the object is brought close to the scintillator in order to adjustthe magnification ratio as described above, the object sometimes entersthe field of view of the imaging means on the incidence surface side. Ifthe object enters the field of view of the imaging means on theincidence surface side, for example, vignetting due to the object isproduced in an image. Therefore, a radiation image acquisition systemcapable of preventing an object from entering the field of view of theimaging means on the incidence surface side while acquiring an image ata desired magnification ratio has been demanded.

It is an object of the present invention to provide a radiation imageacquisition system capable of preventing an object from entering thefield of view of the imaging means on the incidence surface side whileacquiring an image at a desired magnification ratio.

Solution to Problem

A radiation image acquisition system of an aspect of the presentinvention is characterized by including a radiation source emittingradiation toward an object, a holding unit holding the object, awavelength conversion member generating scintillation light in responseto incidence of the radiation emitted from the radiation source andtransmitted through the object, a first imaging means condensing andimaging scintillation light emitted from an incidence surface of theradiation of the wavelength conversion member, a second imaging meanscondensing and imaging scintillation light emitted from a surfaceopposite to the incidence surface of the wavelength conversion member, aholding unit position adjusting means adjusting the position of theholding unit between the radiation source and the wavelength conversionmember, and an imaging position adjusting means adjusting the positionof the first imaging means.

According to this radiation image acquisition system, scintillationlights emitted from the radiation incidence surface of the wavelengthconversion member and its opposite surface are respectively condensedand imaged by the first imaging means and the second imaging means. Thefirst imaging means is an imaging means on the incidence surface side,and the second imaging means is an imaging means on the side opposite tothe incidence surface. By adjusting the position of the holding unitbetween the radiation source and the wavelength conversion member by theholding unit position adjusting means, the object can be brought closeto the wavelength conversion member or moved away from the wavelengthconversion member. By bringing the object close to the wavelengthconversion member, the magnification ratio can be lowered. By moving theobject away from the wavelength conversion member and bringing theobject close to the radiation source, the magnification ratio can beincreased. Here, even when the object is brought close to the wavelengthconversion member, by adjusting the position of the first imaging meansby the imaging position adjusting means, entry of the object into thefield of view of the first imaging means can be prevented. Thus, entryof the object into the field of view of the first imaging means being animaging means on the incidence surface side is prevented, while an imagecan be acquired at a desired magnification ratio.

The imaging position adjusting means rotates the first imaging meanswith a point where an optical axis of the first imaging means and theincidence surface of the wavelength conversion member cross each otherset as a rotation center. According to this arrangement, even when theposition of the first imaging means is adjusted, the optical path lengthfrom the wavelength conversion member to the first imaging means doesnot change. Accordingly, correction to an image becomes easy.

The imaging position adjusting means keeps an angle created by theoptical axis of the first imaging means and the incidence surface of thewavelength conversion member while rotating the first imaging means andthe wavelength conversion member. According to this arrangement, evenwhen the position of first imaging means is adjusted, the angle createdby the optical axis of the first imaging means and the incidence surfaceof the wavelength conversion member is kept fixed, and thus correctionto an image becomes even easier. Also, it is not necessary to frequentlyperform calibration in the first imaging means, so that the convenienceis improved.

The imaging position adjusting means keeps an angle created by anoptical axis of the second imaging means and the opposite surface of thewavelength conversion member while rotating the first imaging means, thewavelength conversion member, and the second imaging means. According tothis arrangement, the first imaging means, the wavelength conversionmember, and the second imaging means integrally rotate with the pointdescribed above set as a rotation center. Accordingly, even when theposition of the first imaging means and the second imaging means isadjusted, the relative positional relationship of the first imagingmeans, the wavelength conversion member, and the second imaging meansdoes not change. Therefore, images for which an inter-image operation iseasily performed can be captured. Also, it is not necessary tofrequently perform calibration in the second imaging means, so that theconvenience is improved.

The above-described radiation image acquisition system includes adetecting means detecting whether the object is in a field of view ofthe first imaging means. According to this arrangement, because whetherthe object is in the field of view of the first imaging means isdetected by the detecting means, the occurrence of “vignetting” in animage can be reliably prevented.

The detecting means detects whether the object is in the field of viewof the first imaging means based on a first image captured by the firstimaging means and a second image captured by the second imaging means.

According to this arrangement, whether the object is in the field ofview of the first imaging means can be accurately detected.

The detecting means detects whether the object is in the field of viewof the first imaging means based on a difference in light intensitybetween the first image and the second image. According to thisarrangement, whether the object is in the field of view of the firstimaging means can be accurately detected.

The detecting means detects whether the object is in the field of viewof the first imaging means based on a difference image between the firstimage and the second image. According to this arrangement, whether theobject is in the field of view of the first imaging means can beaccurately detected.

The detecting means detects whether the object is in the field of viewof the first imaging means based on a ratio of brightness between thefirst image and the second image. According to this arrangement, whetherthe object is in the field of view of the first imaging means can beaccurately detected.

The detecting means detects whether the object is in the field of viewof the first imaging means based on successive images successivelycaptured by the first imaging means while the holding unit is moved bythe holding unit position adjusting means. According to thisarrangement, the point in time where the object has slipped out of thefield of view of the first imaging means or the point in time where theobject has entered the field of view of the first imaging means can beaccurately detected. As a result, the inclination angle of thewavelength conversion member with respect to the radiation source can beminimized, so that an image with little perspective is easily acquired.

The above-described radiation image acquisition system includes an imageoperating means performing an image operation of a first image capturedby the first imaging means and a second image captured by the secondimaging means based on a rotation angle of the first imaging means, thewavelength conversion member, and the second imaging means. According tothis arrangement, a CT (Computed Tomography) image of the object can beacquired.

Advantageous Effects of Invention

According to an aspect of the present invention, entry of an object intothe field of view of the first imaging means being an imaging means onthe incidence surface side can be prevented, while an image can beacquired at a desired magnification ratio.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a radiation image acquisition systemaccording to a first embodiment of the present invention.

FIG. 2 is a perspective view of the radiation image acquisition systemof FIG. 1 from another angle.

FIG. 3 is a plan view of the radiation image acquisition system of FIG.1.

FIG. 4 is a plan view showing a state in which an object is broughtclose to a wavelength conversion member.

FIG. 5 is a plan view showing a state in which the position of a firstimaging means is adjusted.

FIGS. 6A to 6C are examples of images captured by the first imagingmeans.

FIG. 7 is an explanatory view showing rotation angles of the firstimaging means and wavelength conversion member.

FIG. 8 is a view showing an angle changing method by drive of a rotationactuator.

FIG. 9 is a view showing a manual angle changing method.

FIG. 10 is a perspective view of a radiation image acquisition systemaccording to a second embodiment.

FIG. 11 is a perspective view of the radiation image acquisition systemof FIG. 10 from another angle.

FIG. 12 is a plan view of the radiation image acquisition system of FIG.10.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings. In addition, the same elements will bedenoted by the same reference signs in the description of the drawings,and overlapping description will be omitted. Also, the respectivedrawings are prepared for the purpose of description, and are drawn sothat the portions to be described are especially emphasized. Therefore,the dimensional ratios of respective members in the drawings are notalways coincident with actual ratios.

As shown in FIG. 1 to FIG. 3, a radiation image acquisition system 1 ofa first embodiment is a system for acquiring a radiation image of anobject A. The radiation image acquisition system 1 includes a radiationsource 2 that emits radiation such as white X-rays toward the object A,a wavelength conversion plate (wavelength conversion member) 6 thatgenerates scintillation light in response to incidence of the radiationemitted from the radiation source 2 and transmitted through the objectA, a front observation photodetector (first imaging means) 3 thatcondenses and images scintillation light emitted from a radiationincidence surface 6 a of the wavelength conversion plate 6, and a backobservation photodetector (second imaging means) 4 that condenses andimages scintillation light emitted from a back surface 6 b (refer toFIG. 3) that is a surface opposite to the incidence surface 6 a.

The radiation source 2 emits cone beam X-rays from an X-ray emissionspot 2 a. The object A is an electronic component such as asemiconductor device, and is, for example, a semiconductor integratedcircuit. The object A is not limited to a semiconductor device, and maybe food or the like. The object A may even be a film or the like. Theradiation image acquisition system 1 acquires a radiation image of theobject A for the purpose of, for example, a non-destructive analysis ofan industrial product.

The wavelength conversion plate 6 is a tabular wavelength conversionmember, and is, for example, a scintillator such as Gd₂O₂S:Tb,Gd₂O₂S:Pr, CdWO₄, CaWO₄, Gd₂SiO₅:Ce, Lu_(0.4)Gd_(1.6)SiO₅, Bi₄Ge₃O₁₂,Lu₂SiO₅:Ce, Y₂SiO₅, YAlO₃:Ce, Y₂O₂S:Tb, or YTaO₄:Tm. The thickness ofthe wavelength conversion plate 6 is, in a range of several micrometersto several millimeters, set to an appropriate value according to theenergy band of detecting radiation.

The wavelength conversion plate 6 converts X-rays transmitted throughthe object A to visible light. X-rays with relatively low energy areconverted by the incidence surface 6 a that is a front surface of thewavelength conversion plate 6, and is emitted from the incidence surface6 a. Also, X-rays with relatively high energy are converted by the backsurface 6 b of the wavelength conversion plate 6, and is emitted fromthe back surface 6 b.

The front observation photodetector 3 (hereinafter, referred to as a“front surface detector 3”) is an imaging means according to an indirectconversion method that captures a projection image (i.e., a radiationtransmission image) of the object A projected on the wavelengthconversion plate 6 from the side of the incidence surface 6 a of thewavelength conversion plate 6. That is, the front surface detector 3 isan imaging means on the side of the incidence surface 6 a. The frontsurface detector 3 has a condenser lens unit 3 a that condensesscintillation light emitted from the incidence surface 6 a of thewavelength conversion plate 6, and an imaging unit 3 b that imagesscintillation light condensed by the condenser lens unit 3 a. The frontsurface detector 3 is a lens coupling type detector. The condenser lensunit 3 a condenses scintillation light in a field of view 23. As theimaging unit 3 b, for example, an area sensor such as a CMOS sensor or aCCD sensor is used.

The back observation photodetector 4 (hereinafter, referred to as a“back surface detector 4” is an imaging means according to an indirectconversion method that captures a projection image (i.e., a radiationtransmission image) of the object A projected on the wavelengthconversion plate 6 from the side of the back surface 6 b of thewavelength conversion plate 6. That is, the back surface detector 4 isan imaging means on the side of the back surface 6 b. The back surfacedetector 4 has a condenser lens unit 4 a that condenses scintillationlight emitted from the back surface 6 b of the wavelength conversionplate 6, and an imaging unit 4 b that images scintillation lightcondensed by the condenser lens unit 4 a. The back surface detector 4 isa lens coupling type detector, and has the same configuration as that ofthe front surface detector 3 described above. The condenser lens unit 4a condenses scintillation light in a field of view 24 via a mirror 5. Asthe imaging unit 4 b, for example, an area sensor such as a CMOS sensoror a CCD sensor is used.

The mirror 5 reflects light emitted from the back surface 6 b of thewavelength conversion plate 6, and directs the reflected light towardthe back surface detector 4. Exposure to radiation of the back surfacedetector 4 can thereby be prevented.

As shown in FIG. 3, the radiation image acquisition system 1 includes atiming control unit 27 that controls imaging timing in the front surfacedetector 3 and the back surface detector 4, an image processing device28 that is input with image signals output from the front surfacedetector 3 and the back surface detector 4, and executes a predeterminedprocessing such as an image processing based on the respective inputimage signals, and a display device 29 that is input with image signalsoutput from the image processing device 28, and displays a radiationimage. The timing control unit 27 and the image processing device 28 areconstructed by a computer having a CPU (Central Processing Unit), a ROM(Read-Only Memory), a RAM (Random-Access Memory), an input/outputinterface, etc. As the display device 29, a publicly known display isused. In addition, the timing control unit 27 and the image processingdevice 28 may be constructed as programs to be executed by a singlecomputer, or may be constructed as units that are separately provided.

The image processing device 28 has an image acquisition unit 28 a, adetection unit (detecting means) 28 b, and an image processing unit(image operating means) 28 c. The image acquisition unit 28 a is inputwith image signals output from the front surface detector 3 and the backsurface detector 4. The detection unit 28 b detects whether the object Ais within the field of view 23 of the front surface detector 3 based ona radiation image indicated in the image signals input by the imageacquisition unit 28 a. The image processing unit 28 c executes apredetermined processing such as an inter-image operation including adifference operation and an addition operation based on the imagesignals input by the image acquisition unit 28 a. The image processingunit 28 c outputs image signals after the image processing to thedisplay device 29.

As shown in FIG. 1 to FIG. 3, the radiation source 2, the front surfacedetector 3, the back surface detector 4, and the wavelength conversionplate 6 described above are mounted on a plate-like base 10. On one endportion of the base 10, the radiation source 2 is placed, and fixed. Theradiation source 2 has an optical axis X parallel to an extendingdirection of the base 10. On the optical axis X of the radiation source2, the object A and the wavelength conversion plate 6 are disposed. Thatis, the object A is disposed between the X-ray emission spot 2 a of theradiation source 2 and the wavelength conversion plate 6. The object Ais held by a projection angle changing stage (holding unit) 11.

The projection angle changing stage 11 is for holding the object A androtating the object A. Rotating the object A by the projection anglechanging stage 11 allows acquiring radiation images with variousprojection angles. The projection angle changing stage 11 has a drivemechanism (not shown), and rotates the object A about a rotation axis L1by the drive mechanism. The rotation axis L1 is perpendicular to theextending direction of the base 10. The rotation axis L1 intersects theoptical axis X of the radiation source 2, and also passes substantiallythe center of the object A. In addition, the rotation axis L1 is notlimited to the case of passing substantially the center of the object A,and may be located at a position deviated from the object A.

Further, the projection angle changing stage 11 is supported by amagnification ratio changing stage (holding unit position adjustingmeans) 12. The magnification ratio changing stage 12 is for moving theobject A along the optical axis of the radiation source 2 between theradiation source 2 and the wavelength conversion plate 6. Themagnification ratio changing stage 12 moves the object A to change thedistance FOD (Focus-Object Distance) between the radiation source 2(X-ray focus) and the object A, and thereby adjusts a ratio of FOD tothe distance FID (Focus-Image Distance) between the radiation source 2(X-ray focus) and the wavelength conversion plate 6. The magnificationratio of a radiation image can thereby be changed. The projection anglechanging stage 12 is attached to the base 10, and extends parallel tothe optical axis X of the radiation source 2. The magnification ratiochanging stage 12 has a drive mechanism (not shown), and causes asliding movement of the projection angle changing stage 11 between theradiation source 2 and the wavelength conversion plate 6 by the drivemechanism. The moving direction of the projection angle changing stage11 is parallel to the optical axis X of the radiation source 2.

To the other end portion of the base 10, a rotating body 20 that isrotatable with respect to the base 10 is attached. The rotating body 20is supported by a shooting angle changing stage (imaging positionadjusting means) 17. The shooting angle changing stage 17 has a drivemechanism 17 a, and rotates the rotating body 20 about a rotation axisL2 by the drive mechanism 17 a. The rotation axis L2 is parallel to therotation axis L1. The rotation axis L2 is perpendicular to the extendingdirection of the base 10. The rotation axis L2 intersects the opticalaxis X of the radiation source 2, and also passes over the incidencesurface 6 a of the wavelength conversion plate 6. Also, the rotationaxis L2 intersects an optical axis 3 c of the front surface detector 3.That is, the shooting angle changing stage 17 rotates the rotating body20 with a point where the optical axis 3 c of the front surface detector3 and the incidence surface 6 a of the wavelength conversion plate 6cross each other (i.e., a point α to be described later) set as arotation center.

The rotating body 20 has an X-ray protection box 14 that is supported bythe shooting angle changing stage 17, a front surface camera mount 13 onwhich the front surface detector 3 is placed, and an interlocking arm 16that interlocks the X-ray protection box 14 and the front surface cameramount 13.

The X-ray protection box 14 is a casing made of, for example, an X-rayshielding material such as lead, and houses the back surface detector 4.The X-ray protection box 14, by shielding X-rays emitted from theradiation source 2, prevents the back surface detector 4 from beingexposed thereto. In a surface of the X-ray protection box 14 opposed tothe radiation source 2, a quadrangular opening is formed. The wavelengthconversion plate 6 is fitted in the opening to be fixed to the X-rayprotection box 14.

To the interior of the X-ray protection box 14, the back surfacedetector 4 and the mirror 5 are fixed. The mirror 5 has a reflectingsurface that is perpendicular to the extending direction of the base 10and creates 45 degrees with respect to the back surface 6 b of thewavelength conversion plate 6. The condenser lens unit 4 a of the backsurface detector 4 is opposed to the mirror 5. The back surface detector4 has an optical axis 4 c that is parallel to the extending direction ofthe base 10. The optical axis 4 c of the back surface detector 4 isparallel to the back surface 6 b of the wavelength conversion plate 6.That is, the optical axis 4 c is perpendicular to the reflecting surfaceof the mirror 5. The mirror 5 reflects scintillation light emitted fromthe back surface 6 b of the wavelength conversion plate 6, and directsthis light toward the back surface detector 4. In addition, the anglesof the mirror 5 and the optical axis 4 c with respect to the backsurface 6 b of the wavelength conversion plate 6 are not limited to theangles described above, and can be appropriately set. It suffices withan arrangement which enables condensing scintillation light emitted fromthe back surface 6 b of the wavelength conversion plate 6 by the backsurface detector 4.

The interlocking arm 16 extends from the other end portion to the oneend portion of the base 10. That is, the interlocking arm 16 extendsfrom near a side of the wavelength conversion plate 6 in the X-rayprotection box 14 to a side of the radiation source 2. The interlockingarm 16 is disposed at a position so as not to interfere with the opticalaxis X of the radiation source 2. On the front surface camera mount 13,the front surface detector 3 is fixed. Accordingly, the front surfacedetector 3 is disposed lateral to the radiation source 2. In otherwords, the front surface detector 3 is disposed on the same side as thatof the radiation source 2 with reference to a virtual plane that passesthe position of the object A and is perpendicular to the optical axis Xof the radiation source 2. The condenser lens unit 3 a of the frontsurface detector 3 is opposed to the wavelength conversion plate 6. Theoptical axis 3 c of the front surface detector 3 is parallel to theextending direction of the base 10, and is perpendicular to theincidence surface 6 a of the wavelength conversion plate 6. In addition,the angle of the optical axis 3 c with respect to the incidence surface6 a of the wavelength conversion plate 6 is not limited to the angledescribed above, and can be appropriately set. It suffices with anarrangement which enables condensing scintillation light emitted fromthe incidence surface 6 a of the wavelength conversion plate 6 by thefront surface detector 3. In addition, a light receiving surface of theimaging unit 3 b may be substantially parallel to the incidence surface6 a.

Due to the above configuration, the rotating body 20 including thewavelength conversion plate 6, the front surface detector 3, the mirror5, and the back surface detector 4 is rotatable in an integrated mannercentering on the rotation axis L1. That is, the shooting angle changingstage 17 keeps the angle created by the optical axis 3 c of the frontsurface detector 3 and the incidence surface 6 a of the wavelengthconversion plate 6 at 90 degrees, while rotating the front surfacedetector 3 and the wavelength conversion plate 6. Further, the shootingangle changing stage 17 keeps the angle created by the optical axis 4 cof the back surface detector 4 and the back surface 6 b of thewavelength conversion plate 6 at 90 degrees, while rotating the frontsurface detector 3, the wavelength conversion plate 6, and the backsurface detector 4. The shooting angle changing stage 17 changes theangles created by the optical axis 3 c of the front surface detector 3and the optical axis 4 c of the back surface detector 4 with respect tothe optical axis X of the radiation source 2. With the rotation of therotating body 20 by the shooting angle changing stage 17, the field ofview 23 of the front surface detector 3 and the field of view 24 of theback surface detector 4 also rotate.

As above, because the front surface detector 3, the back surfacedetector 4, and the wavelength conversion plate 6 rotate in anintegrated manner, the relative positional relationship of the frontsurface detector 3, the wavelength conversion plate 6, and the backsurface detector 4 does not change. Therefore, images that are acquiredby the front surface detector 3 and the back surface detector 4 areimages for which an inter-image operation is easily performed in theimage processing device 28. Also, because the angles of the frontsurface detector 3 and the back surface detector 4 with respect to thewavelength conversion plate 6 are also fixed, it is not necessary tofrequently perform calibration in the front surface detector 3 and theback surface detector 4, so that the convenience is high.

The optical axis X of the radiation source 2 fixed on the base 10creates an angle θ with respect to a normal B to the incidence surface 6a of the wavelength conversion plate 6. That is, the radiation source 2faces the object A and the incidence surface 6 a, and is disposed at aposition off the normal B to the incidence surface 6 a. In other words,the optical X of the radiation source 2 creates an acute angle withrespect to the incidence surface 6 a. The angle θ changes with arotation of the rotating body 20.

Here, the optical axis X of radiation is a straight line connecting theX-ray emission spot 2 a of the radiation source 2 and an arbitrary pointγ on the incidence surface 6 a of the wavelength conversion plate 6. Inthe present embodiment, the arbitrary point γ is set so as to correspondto a center point of the incidence surface 6 a, and in this case,radiation is irradiated relatively evenly. Also, the normal B is astraight line extending from an arbitrary point α on the incidencesurface 6 a and normal to the incidence surface 6 a. In the presentembodiment, the arbitrary point α is set so as to correspond to a centerpoint of the incidence surface 6 a, and the optical axis X of radiationand the normal B cross each other at the arbitrary point γ (i.e., thearbitrary point α) of the incidence surface 6 a. Of course, thearbitrary point γ and the arbitrary point α are not necessarily a centerpoint of the incidence surface 6 a, or not necessarily the same point.

The optical axis 3 c of the condenser lens unit 3 a of the front surfacedetector 3 is coincident with the normal B to the incidence surface 6 a.The front surface detector 3 is capable of imaging scintillation lightemitted in the direction of normal B to the incidence surface 6 a, andthus easily acquires an image with little perspective. The condenserlens unit 3 a focuses on the incidence surface 6 a, and condensesscintillation light emitted in the direction of normal B from theincidence surface 6 a toward the imaging unit 3 b. In addition, theoptical axis 3 c of the front surface detector 3 may not be coincidentwith the normal B to the incidence surface 6 a.

In this manner, the front surface detector 3 is disposed off the opticalaxis X of the radiation source 2. That is, the front surface detector 3is disposed so as to separate from an emission region of radiation fromthe radiation source 2 (region where a radiation flux 22 exists).Exposure of the front surface detector 3 to radiation from the radiationsource 2 is thereby prevented, which prevents a direct conversion signalof radiation from being generated in the interior of the front surfacedetector 3 to generate noise. Also, the front surface detector 3 isdisposed such that a perpendicular line drawn from the center of thecondenser lens unit 3 a to the incidence surface 6 a of the wavelengthconversion plate 6 is within the range of the incidence surface 6 a, andis disposed over the incidence surface 6 a of the wavelength conversionplate 6. A relatively large amount of scintillation light can thereby bedetected.

The optical axis 4 c of the condenser lens unit 4 a of the back surfacedetector 4 is coincident with a normal C to the back surface 6 b via themirror 5. The back surface detector 4 is capable of imagingscintillation light emitted in the direction of normal C to the backsurface 6 b, and thus easily acquires an image with little perspective.Here, the normal C is a straight line extending from an arbitrary pointβ on the back surface 6 b and normal to the back surface 6 b.Particularly, in the present embodiment, the arbitrary point β is set asa center point of the back surface 6 b, the arbitrary point α on theincidence surface 6 a and the arbitrary point β on the back surface 6 bare located on the same line, and this straight line is coincident withthe normal B and the normal C. The condenser lens unit 4 a focuses onthe back surface 6 b, and condenses scintillation light emitted in thedirection of normal C from the back surface 6 b toward the imaging unit4 b. In addition, the optical axis 4 c of the back surface detector 4may not be coincident with the normal C to the back surface 6 b.

In the radiation image acquisition system 1, the optical path lengthfrom the incidence surface 6 a of the wavelength conversion plate 6 tothe front surface detector 3 is equal to the optical path length fromthe back surface 6 b of the wavelength conversion plate 6 to the backsurface detector 4. In addition, the optical path length from theincidence surface 6 a of the wavelength conversion plate 6 to the frontsurface detector 3 may be different from the optical path length fromthe back surface 6 b of the wavelength conversion plate 6 to the backsurface detector 4. In this case, it is necessary to match the imagesize etc., by an image processing or the like.

As in the foregoing, because the front surface detector 3, the backsurface detector 4, and the wavelength conversion plate 6 rotate in anintegrated manner, each of the optical path length from the incidencesurface 6 a of the wavelength conversion plate 6 to the front surfacedetector 3 and the optical path length from the back surface 6 b of thescintillator 6 to the back surface detector 4 does not change even by arotation of the rotating body 20, and is fixed. Accordingly, correctionto images acquired by each of the front surface detector 3 and the backsurface detector 4 is easy.

Subsequently, the operation of the radiation image acquisition system 1having the configuration described above will then be described. First,control by the timing control unit 27 is performed such that imaging bythe front surface detector 3 and imaging by the back surface detector 4are simultaneously performed. Imaging timing control by the timingcontrol unit 27 allows imaging radiation transmission images of theobject A in different energy bands. In detail, a radiation transmissionimage in a relatively low energy band is imaged by the front surfacedetector 3, and a radiation transmission image in a relatively highenergy band is imaged by the back surface detector 4. Dual-energyimaging is thereby realized. In addition, it is possible in theradiation image acquisition system 1 to control the imaging timings ofthe front surface detector 3 and the back surface detector 4 so as to bedifferent from each other. Also, the front surface detector 3 and theback surface detector 4 may be controlled so as to be different fromeach other in the exposure time and number of shots.

Regarding the function of the front surface detector 3 and the backsurface detector 4, in other words, fluorescence (scintillation light)converted at the side relatively close to the incidence surface 6 a isdetected by the front surface detector 3. Detection of fluorescenceconverted at the incidence surface 6 a-side has features that thefluorescence has little blur and the brightness of fluorescence is high.This is because, in front observation, the influence of diffusion andself-absorption in the interior of the wavelength conversion plate 6 canbe reduced. On the other hand, in the back surface detector 4,fluorescence converted at the side relatively close to the back surface6 b of the wavelength conversion plate 6 is detected. Also in this case,the influence of diffusion and self-absorption in the interior of thewavelength conversion plate 6 can be reduced.

Next, image signals corresponding to radiation images of both front andback surfaces are output to the image processing device 28 by each ofthe front surface detector 3 and the back surface detector 4. When theimage signals output from each of the front surface detector 3 and theback surface detector 4 are input to the image acquisition unit 28 a ofthe image processing device 28, a predetermined processing such as aninter-image operation including a difference operation and an additionoperation is executed based on the input image signals and image signalsafter the image processing are output to the display device 29 by theimage processing unit 28 c of the image processing device 28. Then, whenthe image signals after the image processing output from the imageprocessing device 28 are input to the display device 29, a radiationimage according to the input image signals after the image processing isdisplayed by the display device 29. Particularly, in the imageprocessing device 28, a three-dimensional image of the object A can alsobe prepared by rotating the object A by the projection angle changingstage 11.

Here, according to the radiation image acquisition system 1 of thepresent embodiment, an image of the object A can be acquired at adesired magnification ratio, and further, entry of the object A into thefield of view 23 of the front surface detector 3 can be prevented.Hereinafter, imaging of the object A by the radiation image acquisitionsystem 1 will be described in greater detail with reference to FIG. 3 toFIGS. 6A-FIG. 6C.

As shown in FIG. 3, in a normal shooting state, the object A is disposedwithin the range of cone beam-shaped X-rays emitted from the radiationsource 2 (i.e., within the range of the radiation flux 22). At thistime, the front surface detector 3 is disposed such that the field ofview 23 of the front surface detector 3 does not include the object A.In this case, as shown in FIG. 6A, the shot image Pa has a projectionimage P2 a reflected in the luminescent part P1 of the wavelengthconversion plate 6. As above, when the object A is shot at a certainlevel of magnification ratio, vignetting due to the object A is notproduced.

On the other hand, as shown in FIG. 4, when it is desired to change themagnification ratio or the object A cannot be within a cone beam (i.e.,within the radiation flux 22) because the sample is large, the object Ais moved in a direction to approach the wavelength conversion plate 6 byuse of the magnification ratio changing stage 12. At this time, theobject A sometimes enters the field of view 23 of the front surfacedetector 3. In this case, the object A may block light from thewavelength conversion plate 6. Accordingly, as shown in FIG. 6B, theshot image Pb has not only the projection image P2 b but also vignettingP3 due to the object A reflected in the luminescent part P1 of thewavelength conversion plate 6. As above, the object A enters the fieldof view 23 of the front surface detector 3 when the magnification ratiois lowered, so that vignetting is produced.

Therefore, as shown in FIG. 5, the X-ray protection box 14 is rotated,by use of the shooting angle changing stage 17, centering on the point αwhere the optical axis 3 c of the front surface detector 3 and theincidence surface 6 a of the wavelength conversion plate 6 cross eachother (i.e., the rotation axis L2). At this time, with the rotation ofthe X-ray protection box 14, the front surface detector 3 and the frontsurface camera mount 13 also rotate with the same rotation center by thesame angle through the interlocking arm 16. That is, the rotating body20 rotates. At this time, because the positional relationship of thefront surface detector 3 with the wavelength conversion plate 6 ismaintained, it is not necessary to change calibration conditions. As aresult of thus moving the front surface detector 3 by rotation, as shownin FIG. 6C, the shot image Pc has the projection image P2 c free fromvignetting due to the object A reflected in the luminescent part P1 ofthe wavelength conversion plate 6. As above, by deepening the camerashooting angle of the front surface detector 3, vignetting due to theobject A can be eliminated.

As above, by rotating the front surface detector 3 centering on therotation axis L2 by the shooting angle changing stage 17, entry of theobject A into the field of view 23 of the front surface detector 3 canbe prevented. In the example shown in FIG. 7, the object A is removedfrom the field of view 23 of the front surface detector 3 by furtherrotating the front surface detector 3 by only an angle Δθ from an angleθ.

In the radiation image acquisition system 1, whether the object A is inthe field of view 23 of the front surface detector 3 can be detected bythe detection unit 28 b of the image processing device 28. The detectionunit 28 b detects whether the object A is in the field of view 23 of thefront surface detector 3 by performing various types of processing to bementioned below.

Specifically, the detection unit 28 b can detect whether the object A isin the field of view 23 of the front surface detector 3 based on anincidence surface image captured by the front surface detector 3 and aback surface image captured by the back surface detector 4.

The detection unit 28 b can also detect whether the object A is in thefield of view 23 of the front surface detector 3 based on a differencein light intensity between the incidence surface image and the backsurface image.

The detection unit 28 b can also detect whether the object A is in thefield of view 23 of the front surface detector 3 based on a differenceimage between the incidence surface image and the back surface image.

The detection unit 28 b can also detect whether the object A is in thefield of view 23 of the front surface detector 3 based on a ratio ofbrightness between the incidence surface image and the back surfaceimage.

The detection unit 28 b can also detect whether the object A is in thefield of view 23 of the front surface detector 3 based on successiveimages of the incidence surface successively captured by the frontsurface detector 3 while the projection angle changing stage 11 is movedby the magnification ratio changing stage 12.

According to the radiation image acquisition system 1 of the presentembodiment described above, scintillation lights emitted from theincidence surface 6 a and the back surface 6 b of the wavelengthconversion plate 6 are respectively condensed and imaged by the frontsurface detector 3 and the back surface detector 4. By adjusting theposition of the projection angle changing stage 11 between the radiationsource 2 and the wavelength conversion plate 6 by the magnificationratio changing stage 12, the object A can be brought close to thewavelength conversion plate 6 or moved away from the wavelengthconversion plate 6. By bringing the object A close to the wavelengthconversion plate 6, the magnification ratio can be lowered. By movingthe object A away from the wavelength conversion plate 6 and bringingthe object A close to the radiation source 2, the magnification ratiocan be increased. Here, even when the object A is brought close to thewavelength conversion plate 6, by adjusting the position of the frontsurface detector 3 by the shooting angle changing stage 17, entry of theobject A into the field of view 23 of the front surface detector 3 canbe prevented. Thus, entry of the object A into the field of view 23 ofthe front surface detector 3 being an imaging means on the incidencesurface side can be prevented, while an image can be acquired at adesired magnification ratio. Also, the occurrence of vignetting due tothe object A can be prevented.

Because the shooting angle changing stage 17 rotates the front surfacedetector 3 with the point α where the optical axis 3 c of the frontsurface detector 3 and the incidence surface 6 a of the wavelengthconversion plate 6 cross each other set as a rotation center, even whenthe position of the front surface detector 3 is adjusted, the opticalpath length from the wavelength conversion plate 6 to the front surfacedetector 3 does not change. Accordingly, correction to an image is easy.

Even when the position of the front surface detector 3 is adjusted, theangle created by the optical axis 3 c of the front surface detector 3and the incidence surface 6 a of the wavelength conversion plate 6 iskept fixed, and thus correction to an image becomes even easier. Also,it is not necessary to frequently perform calibration in the frontsurface detector 3, so that the convenience is improved.

The front surface detector 3, the wavelength conversion plate 6, and theback surface detector 4 integrally rotate with the point α describedabove set as a rotation center. Accordingly, even when the position ofthe front surface detector 3 and the back surface detector 4 isadjusted, the relative positional relationship of the front surfacedetector 3, the wavelength conversion plate 6, and the back surfacedetector 4 does not change. Therefore, images for which an inter-imageoperation is easily performed can be captured. Also, it is not necessaryto frequently perform calibration in the back surface detector 4, sothat the convenience is improved.

Conventionally, when the object A is large-sized or has a lowmagnification ratio (i.e., the object A is close to the wavelengthconversion plate 6), the object A overlaps the field of view 23 of thefront surface detector 3, and the shootable area has consequently beenlimited. According to the radiation image acquisition system 1, theshootable area can be widened by widening the angle range in which theoptical axis 3 c can be moved.

By making the angle created by the optical axis X of the radiationsource 2 and the optical axis 3 c of the front surface detector 3 to aminimum when the object A is small, the influence of “vignetting” due toan inclination of the wavelength conversion plate 6 can be reduced, anda loss or decline in resolution can be reduced as much as possible.

Because whether the object A is in the field of view 23 of the frontsurface detector 3 is detected by the detection unit 28 b, theoccurrence of vignetting in an image can be reliably prevented.

The detection unit 28 b detects whether the object A is in the field ofview 23 of the front surface detector 3 based on an incidence surfaceimage captured by the front surface detector 3 and a back surface imagecaptured by the back surface detector 4. This allows accuratelydetecting whether the object A is in the field of view 23.

The detection unit 28 b can also detect whether the object A is in thefield of view 23 of the front surface detector 3 based on a differencein light intensity between the incidence surface image and the backsurface image. This allows accurately detecting whether the object A isin the field of view 23.

The detection unit 28 b can also detect whether the object A is in thefield of view 23 of the front surface detector 3 based on a differenceimage between the incidence surface image and the back surface image.This allows accurately detecting whether the object A is in the field ofview 23.

The detection unit 28 b can also detect whether the object A is in thefield of view 23 of the front surface detector 3 based on successiveimages of the incidence surface successively captured by the frontsurface detector 3 while the projection angle changing stage 11 is movedby the magnification ratio changing stage 12. This allows accuratelydetecting the point in time where the object A has slipped out of thefield of view 23 of the front surface detector 3 or the point in timewhere the object A has entered the field of view 23 of the front surfacedetector 3. As a result, the inclination angle of the wavelengthconversion plate 6 with respect to the radiation source 2 can beminimized, so that an image with little perspective is easily acquired.

Meanwhile, when the radiation image acquisition system 1 is an X-ray CTsystem, information on the angles with respect to the optical axis X ofthe radiation source 2 and the incidence surface 6 a of the wavelengthconversion plate 6 becomes necessary. In the radiation image acquisitionsystem 1, because the angle of the incidence surface 6 a of thewavelength conversion plate 6 and the optical axis 3 c of the frontsurface detector 3 is kept fixed, by determining the angle of theoptical axis X of the radiation source 2 and the optical axis 3 c of thefront surface detector 3, a CT image can be acquired.

Specifically, as shown in FIG. 8, the angle can be changed by drivingthe drive mechanism 17 a that is a rotation actuator. In this case, ashot image is checked (visual or algorithmic detection is performed),and the angle of the front surface detector 3 is changed to reach aposition where the object A is not reflected in the image. Then, theangle at that time is detected. Changing the angle of the wavelengthconversion plate 6 and the front surface detector 3 by the drivemechanism 17 a allows obtaining the changed angle by, for example, a PC30 connected to the drive mechanism 17 a. The angle between the opticalaxis X and the optical axis 3 c can thereby be obtained.

Also, as shown in FIG. 9, the angle can also be manually changed. Inthis case, by disposing the wavelength conversion plate 6 and the frontsurface detector 3 on a graduated rotating stage (imaging positionadjusting means) 17A and reading the graduation when the angle wasmanually changed, the angle between the optical axis X and the opticalaxis 3 c can be obtained.

In these cases, the image processing unit 28 c of the image processingdevice 28 can perform an image operation of the incidence surface imageand the back surface image based on a rotation angle of the frontsurface detector 3, the wavelength conversion plate 6, and the backsurface detector 4. According to the image processing device 28including the image processing unit 28 c, a CT image of the object A canbe acquired.

Next, a radiation image acquisition system 1A of a second embodimentwill be described with reference to FIG. 10 to FIG. 12. The differencein the radiation image acquisition system 1A shown in FIG. 10 to FIG. 12from the radiation image acquisition system 1 of the first embodiment isthe point of adopting a rotating body 20A having a vertical X-rayprotection box 14A in place of the rotating body 20 having thehorizontal X-ray protection box 14. In the vertical X-ray protection box14A, the disposition itself of the wavelength conversion plate 6 has notbeen changed from that of the radiation image acquisition system 1, butthe disposition of a mirror 5A and a back surface detector 4A has beenchanged. That is, the optical axis 4 c of the back surface detector 4Ais perpendicular to the extending direction of the base 10. The mirror5A has a reflecting surface that is inclined at 45 degrees with respectto the extending direction of the base 10. In addition, similar to theradiation image acquisition system 1, the radiation image acquisitionsystem 1A also includes a timing control unit 27, an image processingdevice 28, and a display device 29.

Also according to such a radiation image acquisition system 1A, theposition of the front surface detector 3 can be adjusted by rotating therotating body 20A centering on the rotation axis L2. Thus, the sameadvantageous effects as those of the radiation image acquisition system1 can be provided.

As above, the embodiment of the present invention has been described,but the present invention is not limited to the above-describedembodiment. In the above-described embodiment, a description has beengiven of the case where the front surface detector 3 rotates centeringon the rotation axis L2, but the front surface detector 3 may rotatecentering on another rotation axis. The other rotation axis may pass anintersection of the optical axis 3 c of the front surface detector 3 andthe incidence surface 6 a of the wavelength conversion plate 6, but maynot pass the intersection. The movement of the front surface detector 3is not limited to a rotational movement, and may be a sliding movement.Whether the object A is in the field of view 23 of the front surfacedetector 3 may be detected by other means. For example, a dedicateddetector may be used separately.

INDUSTRIAL APPLICABILITY

According to an aspect of the present invention, entry of an object intothe field of view of the first imaging means being an imaging means onthe incidence surface side can be prevented, while an image can beacquired at a desired magnification ratio.

REFERENCE SIGNS LIST

1, 1A . . . radiation image acquisition system, 2 . . . radiation source(radiation source), 3 . . . front observation photodetector (firstimaging means), 3 c . . . optical axis, 4 . . . back observationphotodetector (second imaging means), 4 c . . . optical axis, 6 . . .wavelength conversion plate (wavelength conversion member), 6 a . . .incidence surface, 6 b . . . back surface (surface on the oppositeside), 11 . . . projection angle changing stage (holding unit), 12 . . .magnification ratio changing stage (holding unit position adjustingmeans), 17 . . . shooting angle changing stage (imaging positionadjusting means), 23 . . . field of view (field of view of first imagingmeans), 28 b . . . detection unit (detecting means), 28 c . . . imageprocessing unit (image operating means), A . . . object, α . . . point.

1-11. (canceled)
 12. A system for capturing a radiation image of anobject, the system comprising: a wavelength converter configured togenerate scintillation light in response to incidence of radiationtransmitted through the object; a first imaging device configured tocapture an image of scintillation light emitted from an incidencesurface of the wavelength converter; an adjusting device configured toadjust a position of the first imaging device.
 13. The system accordingto claim 12, wherein the adjusting device is configured to rotate thefirst imaging device.
 14. The system according to claim 13, wherein theadjusting device is configured to rotate the first imaging device so asto maintain an angle formed between an optical axis of the first imagingdevice and the incidence surface of the wavelength converter.
 15. Thesystem according to claim 14, wherein the angle is 90°.
 16. The systemaccording to claim 12, wherein the adjusting device has a rotation axison the incidence surface of the wavelength converter.
 17. The systemaccording to claim 16, further comprising a radiation source configuredto emit radiation toward the object, wherein the rotation axisintersects with an axis of the radiation source.
 18. The systemaccording to claim 16, wherein the rotation axis intersects with anoptical axis of the first imaging device.
 19. The system according toclaim 12, further comprising a second imaging device configured tocapture an image of scintillation light emitted from a surface oppositeto the incidence surface of the wavelength converter.
 20. The systemaccording to claim 12, wherein the radiation is X-ray.
 21. The systemaccording to claim 12, wherein the wavelength converter comprises ascintillator.
 22. A method for capturing a radiation image of an object,the method comprising: adjusting a position of a first imaging device,irradiating the object with radiation emitted from a radiation source;converting the radiation transmitted through the object to scintillationlight by a wavelength converter; capturing an image of the scintillationlight emitted from an incidence surface of the wavelength converter bythe first imaging device.
 23. The method according to claim 22, whereinthe adjusting rotates the first imaging device.
 24. The method accordingto claim 23, wherein the adjusting rotates the first imaging device soas to keep an angle based on an optical axis of the first imaging deviceand the incidence surface of the wavelength converter.
 25. The methodaccording to claim 24, wherein the angle is 90°.
 26. The methodaccording to claim 22, wherein the adjusting rotates the first imagingdevice on a rotation axis on the incidence surface of the wavelengthconverter.
 27. The method according to claim 26, wherein the rotationaxis intersects with an axis of the radiation source.
 28. The methodaccording to claim 26, wherein the rotation axis intersects with anoptical axis of the first imaging device.
 29. The method according toclaim 22, further comprising capturing an image of scintillation lightemitted from a surface opposite to the incidence surface of thewavelength converter.
 30. The method according to claim 22, wherein theradiation is X-ray.
 31. The method according to claim 22, wherein theconverting is performed with the wavelength converter comprising ascintillator.
 32. A method of manufacturing an image capturing system,the method comprising: assembling components of the image capturingsystem; adjusting the image capturing system, wherein the adjustingcomprises: disposing a wavelength converter on an optical axis of aradiation source; adjusting a position of a first imaging device withrespect to an incidence surface of the wavelength converter, whereby theassembling and the adjusting results in an adjusted image capturingsystem.